In general, when a silver halide photographic emulsion is coated on a support, a spectral sensitizing dye having the necessary absorption wavelength is added to the emulsion so that it is spectrally sensitized.
Examples of such sensitizing dyes which may be used for spectral sensitization include water-insoluble dyes and water-soluble dyes containing water-soluble groups. However, water-soluble dyes are disadvantageous in that they have a weak adsorption to grains and thus have a low color sensitivity compared to water-insoluble dyes. In contrast, water-soluble dyes are less subject to color remaining after processing than water-insoluble dyes. Thus, it has been very difficult to meet both the requirements for color sensitization and color remaining at the same time. Heretofore, color sensitivity has often had priority to color remaining. Thus, water-insoluble sensitizing dyes have generally been used.
It has been known that photographic sensitivity can be improved by incorporating a polyoxyethylenic compound in at least one layer in the photographic light-sensitive material. However, the sensitizing effect of the polyoxyethylenic compound has not been as high as expected in emulsion grain systems which include a large amount of a water-insoluble sensitizing dye, especially upon high speed development.
Nevertheless, no other compound has been found which surpasses the polyoxyethylenic compounds in sensitizing effect. Therefore, the best sensitizing method is to make the best use of the effect of the polyoxyethylenic compound.
Accordingly, studies have focused primarily on finding a suitable sensitizing dye and spectral sensitizing method which makes the best use of the sensitizing effect of polyoxyethylenic compounds.
Methods for adding a sensitizing dye to a photographic emulsion before chemical sensitization are known. For example, U.S. Pat. No. 4,425,426 discloses methods for adding a sensitizing dye to a photographic emulsion prior to or during chemical sensitization. Methods for adding spectral sensitizing dyes to photographic emulsions before the completion of the formation of silver halide grains are disclosed in U.S. Pat. Nos. 2,735,766, 3,628,960, 4,183,756 and 4,225,666.
Specifically, U.S. Pat. Nos. 4,183,756 and 4,225,666 disclose that the addition of a spectral sensitizing dye to a photographic emulsion after the formation of a stable nucleus of silver halide grains provides the advantages of improving the photographic sensitivity and intensifying the adsorption of a spectral sensitizing dye to silver halide grains.
In the above-described methods, the chemical sensitization is achieved in the presence of a spectral sensitizing dye. In such cases, however, the photographic sensitivity is often lowered or remains about the same due to the presence of the spectral sensitizing dye.
The inventors of the present invention have found that the combined use of a water-soluble sensitizing dye as a spectral sensitizing dye, silver halide grains which have been chemically sensitized in the presence of the spectral sensitizing dye, and a polyoxyethylenic compound, or the combined use of silver halide grains, a water-soluble sensitizing dye which is added to a chemically sensitized silver halide emulsion containing the silver halide grains prior to its coating and a polyoxyethylenic compound can provide for high sensitivity silver halide photographic materials having excellent development capabilities at high speeds and which are less subject to color remaining after processing. The inventors have also found that in such materials, the photographic sensitivity and development capabilities at high speeds are much the same as those emulsions to which the spectral sensitizing dye is added immediately before coating.